1. Field of the Invention
The invention relates to methods and apparatus useful for the fusion of two or more adjacent vertebrae. The present invention incorporates novel devices to facilitate placement of screws and plates to stabilize the vertebrae, and a novel system for the parallel decortication of the vertebral endplates prior to insertion of the bone graft.
2. Description of the Background
Spinal fusion is commonly used in the treatment of a number of disorders of the spinal column, both in man and animals. Spinal fission may be used to immobilize motion segments in the spine that are diseased or require stabilization due to a number of conditions, such as trauma, spinal stenosis, disc herniation, infection, tumors, spondylolisthesis, post-laminectomy and others.
During the vertebral fusion procedure, the intervertebral disc is removed and a bone graft or other graft material is placed between the contiguous vertebrae, which may then be stabilized using a suitable implant, such as a plate. To maximize the formation of a strong callus between the fused vertebrae, the endplates of the two vertebrae are decorticated prior to insertion of the graft. Decortication is a tedious but important part of the surgical procedure. Due to the close proximity of the spinal cord and other fragile structures to the surgical site, a reliable system is needed to prepare the vertebrae for fusion, including decortication of the vertebrae and preparation of the vertebrae for the installation of the fixation plate.
There are a number of methods and devices that have been used to facilitate stabilization or repair of damage to the spinal column. There are also a number of devices which are useful to prepare the bones of the spinal column and other joints to receive implants or fixation devices. For example, artificial discs have been used to replace damaged human intervertebral discs. In one such procedure, a router guide is first used to cut elongate channels into the bodies of the two adjacent vertebrae to receive the cylindrical shaped members of the implant. In this procedure, an artificial disc is used to replace the damaged intervertebral disc, as opposed to a fusion procedure in which the disc is removed and the vertebrae are fused to each other. (U.S. Pat. No. 5,246,458). In another procedure using a disc endoprosthesis, concave surfaces are cut in the inferior and superior surfaces of the opposing vertebral bodies using a bone surface milling jig (jig not shown), prior to implantation of the endoprosthesis. (U.S. Pat. No. 5,865,846). In still another procedure using a spinal fusion implant, two cylindrical cavities are reamed immediately next to one another within the disc space. A cylindrical reamer is passed through a tubular guide laparoscopically. (U.S. Pat. No. 5,489,307 and U.S. Pat. No. 5,700,291).
In addition to methods using artificial implants in the intervetebral spaces, other devices have been developed to facilitate surgical manipulation of the vertebrae. For example, a drill and tap guide system has been used to make screw holes in vertebrae to be instrumented (U.S. Pat. No. 5,423,826). Template assemblies have been used to mark locations on the disc annulus for implantation of an interbody fusion device or introducing a working instrument (U.S. Pat. No. 5,645,549 and U.S. Pat. No. 5,785,707). In addition, a spinal transpedicle drill jig has been used to provide a safe route for drilling screw holes through the pedicles of the vertebrae (U.S. Pat. No. 4,907,577). However, none of these devices is suitable for nor provides a method or apparatus for the parallel decortication of the vertebral endplates prior to spinal fusion with a bone implant (or other bone-like implant capable of promoting fusion), and more specifically, one in which means are provided to prevent damage to the spinal cord.
With respect to other areas of the body, a number of devices have been developed to facilitate the removal of bone before implantation of a fixation device or other surgical manipulation. One such procedure utilizes an orthopedic cutting guide and bushing having a bore therethrough to prepare a femur for knee revision surgery (U.S. Pat. No. 5,735,856).
In another procedure involving the femur, a dual slide cutting guide which accommodates a milling burr is used in milling planar surfaces on a femur (U.S. Pat. No. 5,653,714). With respect to preparation of the tibia, a template may be used to mill planar surfaces on the articular surface of the tibia. A pivot arm is used to guide the depth of the cutting burr, thereby creating a planar cut in the bone surface (U.S. Pat. No. 5,344,423).
Another device for preparing the knee incorporates a saw guide, including a constrained slot for guiding the saw, useful for making cuts in the bones of the knee joint during prosthesis implantation surgery (U.S. Pat. No. 5,415,663). The foregoing devices, although quite useful in preparing the long bones of the legs, are not suitable for use on the vertebral column, and more particularly, for use in the decortication of the vertebral endplates.
The invention overcomes the problems and disadvantages associated with current strategies and designs, and provides a novel system to facilitate decortication of the vertebral endplates and the fusion of adjacent vertebrae. The system employs a targeter which allows proper placement of a plurality of vertebral screws in the vertebral bodies. A distractor is then temporarily attached to the vertebral screws, and the disc space is distracted. A bushing is then inserted between the two arms of the distractor. The bushing acts as a router guide for a cutting bit, to allow the perfect parallel decortication of the vertebral endplates. At this juncture, surgical decompression of the spinal nerve roots or the spinal cord may be undertaken if indicated, using conventional methods. After insertion of a bone graft, a plate is affixed to the vertebral screws using locking screws, further stabilizing the joint so that fusion may occur.
One embodiment of the invention is directed to a spinal fusion instrument system or assembly comprising a bushing, which defines an opening, and means for mounting the bushing on two contiguous vertebrae. The opening in the bushing is configured to guide a cutting tool to allow parallel decortication of the opposing endplates of the two contiguous vertebrae. Preferably, the opening defined by the bushing has two parallel sides which are disposed parallel to the opposing endplates when the bushing is mounted on the contiguous vertebrae.
Another embodiment is directed to an apparatus for guiding a cutting tool to prepare two contiguous vertebrae for fusion to each other comprising a bushing, which defines a first hole therethrough, and a mounting member for mounting the bushing on the two contiguous vertebrae. The hole of the bushing is configured to guide the cutting tool during decortication of opposing endplates of the two contiguous vertebrae.
Another embodiment is directed to an apparatus for guiding a cutting tool to prepare two contiguous vertebrae for fusion to each other comprising a bushing, which defines a first hole therethrough, and a means for mounting the bushing on the two contiguous vertebrae. The hole of the bushing is configured to guide the cutting tool during decortication of opposing endplates of the two contiguous vertebrae.
Another embodiment is directed to a method for preparing two vertebrae for spinal fusion comprising placing a first vertebral screw and a second vertebral screw into the anterior aspect of a first vertebral body, placing a third vertebral screw and a fourth vertebral screw into the anterior aspect of a second vertebral body, the first and the second vertebral bodies being contiguous to each other, mounting a distractor on the first, second, third and fourth vertebral screws, the distractor comprising two distractor arms, distracting the disc space between the two vertebrae, mounting a bushing between the two distractor arms, the bushing defining a first guide hole therethrough, inserting a cutting tool through the guide hole to cut away the target tissue, and removing the target tissue. The method may also comprise the step of surgically decompressing the spinal nerve roots or spinal cord, if indicated, using conventional means.
Another embodiment is directed to a method for fusing two contiguous vertebrae to each other comprising placing a first vertebral screw and a second vertebral screw into an anterior aspect of a first vertebral body, placing a third vertebral screw and a fourth vertebral screw into an anterior aspect of a second vertebral body, the first and the second vertebral bodies being contiguous to each other, mounting a distractor on the first, second, third and fourth vertebral screws, the distractor comprising two distractor arms, distracting the disc space between the two vertebrae, mounting a bushing between the two distractor arms, the bushing defining a first guide hole therethrough, inserting a cutting tool through the guide hole to cut away the target tissue, removing the target tissue, placing a bone graft between the first and second vertebral bodies, and allowing the two contiguous vertebrae to fuse. In a preferred embodiment, the method further comprises the step of stabilizing the first and second vertebral bodies and bone graft with a fixation plate. The method may also comprise the step of surgically decompressing the spinal nerve roots or spinal cord, if indicated.
Another embodiment is directed to a method for guiding a cutting tool during removal of a target portion of a bone comprising the steps of mounting a bushing on the bone, the bushing defining an opening therethrough which is sized to restrict passage of a collar on the cutting tool, inserting the cutting tool through the opening, and cutting away the target portion.
Other objects and advantages of the invention are set forth in part in the description which follows, and in part, will be obvious from this description, or may be learned from the practice of the invention.